Process for the separation of iron from other metals accompanying iron in ores or waste materials



May 27, 1958 D. H. FASTJE ET AL 2,835,487

PROCESS FOR TEE SEPARATION OE IRON FROM OTHER METALS AOOOMPAMTING IRON IN oREs OR wAsTE MATERIALS Filed Jan. 51, 195e I QQN @wub @E E@ was:

.Gsm w www@ mam United States Patent O PROCESS FOR THE SEPARATION OF IRON FROM OTHER METALS ACCOMPAYING IRON 1N GRES OR WASTE MATERlALS Dietrich H. Fastje, Hannover, and Rudolph H. Gerlach and Otto K. Vorwerk, Rheinhausen, Germany, assignors to Aktiengesellschaft fr Unternehmungen der Eisenund Stahlindustrie, Essen, Germany Application January 31, H56, Serial No. 562,544 Claims priority, application Germany January 31, 1%55 9 Claims, (Cl. 7S- 41) This invention relates to a new process for the separation of iron from other metals accompanying iron in ores or waste materials, which accompanying metals are volatilized during the reduction of the iron.

It is an object of our invention to provide a process for separating the iron from other metals accompanying iron in ores or waste materials in such a manner that the iron, as well as such other metals, particularly lead and zinc, can be obtained economically.

It is further object of our invention to provide a new process for obtaining iron and such volatilizable metals as lead and zinc accompanying the iron, thereby avoiding detrimental influences due to the presence of lead or zinc in the ores, on the course of the process and the installation for the Same.

it is another object of our invention to provide a new process permitting the use of a blast furnace for obtaining iron and volatilizable metals such as zinc, lead, cadmium, germanium, thallium and the allotropic modiications of metallic nature of selenium and tellurium accompanying the iron in quantities up to 10% of the ironcontaining ore.

It is a still further object of our invention to provide a process of the above-stated nature which can be carried out as a closed cycle of steps so directed that the losses of iron and other metals are kept low without requiring any costly preliminary treatments.

It is finally an object of our invention to provide a new continuously operating process for separating iron and volatilizable metals accompanying iron in ores and waste materials from one another.

It is well known in the art of producing iron that many iron ores and, in particular, fine ores, can not be economically processed and render the optimum profits, because of the drawback that these ores contain volatilizable metals accompanying the iron such as, for instance, lead and zinc. On the one hand, these ores are undesirable or can not be used as charge components for blast furnaces in the production of iron, since the accompanying metals unfavorably influence the process in the blast furnace.

For instance, zinc, as an accompanying metal, accumulates in the flue dust. Therefore, when the latter is sintered or briquet'ted to convert'the dust to lumps which are then reintroduced into the blast furnace cycle, this will lead to an increase in the zinc content of the smelting charge which, in turn, results in` disturbances in the blast furnace process, for instance, by deposits formed in the shaft or at the gas outlet or liue at the top of the furnace. It is, however, preferred, from an economic viewpoint, in the art of making iron in a blast furnace ICC to return the entire flue dust and slurries obtained from the latter to the blast furnace, It has, therefore, generally been considered undesirable and disadvantageous to smelt ores containing more than 2% zinc and/or other volatilizable metals in the furnace without unduly shortening its life time. On the other hand, the content of lead and zinc in these ores is in most cases too low to warrant an economical processing of these ores for the purpose of producing these metals alone without obtaining at the same time the iron contained therein.

Our present invention provides for the processing of the aforesaid kind of ores and for obtaining iron as well as the volatilizable metals such as lead and zinc accompanying the iron in the ores, in an economical manner while avoiding the above-described eiects on the course of the process in the blast furnace or on the blast furnace itself. This is achieved by carrying out, in the process according to the invention, the separation of iron from the volatilizable metals accompanying iron in the ores or in iron containing waste materials in two steps, the rst step comprising smelting the ores and/ or waste materials in the blast furnace under reduction to pig iron, and the second step of reducing the line dusts from the blast furnace and line sludge that can be obtained from these dusts by Various known processes, which dusts and sludge contain a portion of iron as well as the volatilizable metals, in a rotary kiln whereby the .iron compounds are reduced to iron and the volatiiizable metals are obtained from the gases released during the second stepV by a number of further steps known per se.

It is an advantage of our new process that the treatment of the ilue dust, having a high zinc content, in a rotary kiln subsequent to the smelting step in the blast furnace makes it possible to smelt even roasted pyrites containing up to 8-10% of zinc in limited quantities in the blast furnace.

in the first step of our process which is carried out in the blast furnace, the major part of the iron contained in the ore is converted to pig iron and removed from the process, while a minor portion of the iron is transferred to the flue dusts or to the sludge obtained from the flue gases, depending upon the methods employed for purifying the flue gases. The aforesaid iiue dusts or flue sludge derived from the blast furnace process contain, apart from the above-mentioned small quantity of iron, substantially all lead and zinc originally contained in the ores as well as carbon in quantities not exceeding a few percent which are derived from the blast furnace leaving the same with the flue gases in the form of tine coke dust.

The second step of our process comprises the reduc-y tion of the flue dust or flue sludge resulting from the first step, which reduction is carried out, for instance, according to the well known Krupp Direct irocess, which consists in mixing the charge for this process with finegrained reduction carbon and introducing the resulting mixture into a rotary kiln whereby solid iron in the shape of nodules is obtained.

The accompanying metals such as lead or zinc are volatilized in the rotary kiln and leave the same in the flue gases from which they are practically completely recovered in the form of their oxides. This recovery step is carried out in a manner wellknown in the art.

It is, for instance, described in Victor Tafels Lehrbuchder Metallhttenkuride, vol. II (1953), pp.V 637-641.

Subsequently, these metal oxides may be used to prepare pigments or for the production of the metals propere;v

The iron nodules obtained by this second process step in the rotary kiln can be returned to the blast furnace to I .be incorporated in the chargel for a new process step.-

It is also of advantage to add to the Hue dusts or flue sludges obtained from the ue dusts diiculty reducible materials such as roasted pyritic materials, purple ore, and the like, and then process the resulting mixture in the rotary kiln according to the second step of our process, as the reduction of the latter materials will be facilitated by the admixture of the more easily reducible dust or siudge. The generally'relatively high calcium oxide 'content of sludges obtained from ue dusts makes it possible to apply the Krupp direct process to the treatment of waste materials from foundries, steel works, etc., which materials are rich in silicic acid. (The Krupp direct process is disclosed in Patents No. 1,964,917; 2,026,683; 2,709,650 and 2,721,794.) The CaO content of the flue dust is always so high VthatV it is urlsuitedl for obtaining the kind of slag required in a rotary kiln. Therefore, the admixture Yof materials such as roasted pyrites, which usually have aV high content of silicic acid, is of advantage.' If the roasted pyritesV are not sutiiciently'rich in silicic acid toachievethe desired slag composition in the rotary kiln, a further admixture of ores rich in silicic acid is required. On the other hand, if the materials admixed to the iiuel dust are so rich in silicic acid that the slag composition in theV rotary kiln would have too low ak Caocoutent, the addition of further calcium oxide is required.

In a further modification of the process according to ourfinvention, when Vthe iron content of the materials to be subjected to the second processstep is low, i. e. below Fe, we propose to add fineV ores rich in iron content (about 40% Fe) to the charge in therotary kiln in orderV Forv to make this process stepY still more economical. this purpose, We prefer Vto use'iron ores having a relativelyhigh content of silicic acid, if this should be required, in order to obtain a slag of aV correspondingly siliceous composition, while we use ores of a more basic nature if otherwise the resulting slag would vbe too'acid. VAccording Vto yet another modification of the'process accordingto our invention, if the charge for the irotary kiln derived from the rst step has too low a content of volatilizable metals Vsuch asV lead or zinc, we use fine ores, either of acid or basic nature, lhaving a relatively high content of such volatilizable metals as an addition to the charge for the second step of our process, thereby increasing the content of these volatilizable metals 'in the total charge to be subjected toour second process step,

while at the same time influencing the composition'of the resulting slag in the manner described'above.

The volatilizable metals Yreferred to in this process comprise, as has been mentioned above, lead Vand zinc,

as well as cadmium, germanium, thallium, metallicmo'di cations of selenium and tellurium.

A preferred embodiment of the process shall be de- Y scribed hereinafter in detail in the accompanying flow sheet. Step I is carried out in the blast furnace and step II in the rotary kiln. The blast furnace is charged with a smelting mix of roasted pyrites containing from 1%V Zn and 60% Fe to 11% Zn and 43% Fe. In order to prepare the charge for theblast furnace the roasted pyrites and thev coarser share of the dry ue dust from a Y preceding blastrfurnace operation are mixed and sintered in a sintering furnace. The coarse ue'dust contains from about 0.3% zinc and 43% iron to 0.5% zinc and 38% iron; The Vsintered product is thenV crushed and mixed with iron ore containing from traces to about 0.5 of zinc, and with lime stoneY and coke, and the resulting Vsmelting charge is 'introduced into the blast furnace.V 'f

VThe ratios of roasted'pyritesto coarse ue dust in the sinter'products may vary over awide range as long asV the total zinc content of the 'sinter products does` not substantially exc`eed'10%.Y The ratio. of thesinter prod- VuctsV to lthe fresh irouoresandthe othen components l in the smelting charge mayk equally vary over a wide range.

A preferred ratio of sinter-products to ores -is from 1:1 to V1:3. Y

The flue gases and flue dust escaping from the blast Vfurnace are introduced into a cyclone dust catcher in which the coarser particles of the flue dust containing from 0.3 to 0.5% Zn and Vfrom 38 to 43% Fe are separated from the ner flue dust containing from 2% Zn and Fe to 20% Zn and 16% Fe.

The coarse ue dust is returned to the blast furnace.

The tine ue dust is passedthrough a washing plant.

from which the purified gases escape for eventual use as heating gas, while the flue dust is converted into a` slurry of the'same zinc and iron content as theaforementioned ne flue dust.

If a dry purication plant, such as a lter, is used for purifying the ue gas, the fineA flue dust isretained in a v dry state.Y Y

The slurry or fine dust is mixed withr'oasted pyrites having'a high zinc content, inthe order of 1 to 11% and an liron content from 43 to 60%, as wellias' ironY ore having a high content of SiOZ for regulating the composi- Y tion of the resulting slag.. Iron Ypresfcontaining CaO and ySiO2 in a ratio below3:10 may be considered as having Va high content of silicic acid. The ratio :of roasted pyrites to flue dust (or ue slurry) is,for' instance, inthe order of 10:6 to 10:12.V However, these ratios are not particularly critical.' `In apreferred Yexample to be described hereinafter in detail We usea ratio of iiue Vdust to pyrite of 1:1V Vin the kiln charge. The amount of iron ore of high silicic acid content de# pends upon the degree of acidity desired in the slag ob tained from the kiln and on the exact SiO2 content of the ore. In the examples described hereinafter Vwe use a content of ore inthe charge. amounting to 8-10%.

k'l'he entire contentof volatilizable metals leaves the rotary kiln with the ue gases ofthe latter, mainly inA the form of metal oxides. Theiiue gases anddust from separating plant.

of a powder containing approximately 70% ZnO. The

recovery of lead and other volatilizable metals is carried out in the same manner.

The process according to our invention is further illustrated by thefollowing examples: Y

Example I Step 1.-A smelting charge for the v*blast furnace is prepared for obtaining a smelt of 1000 kilograms of pig iron. This chargehas the following composition:v f

535 kg.Y sinter products, consisting Vof 1 fpyrites'and 2 parts ofcoarse ue dust 811kg. Swedish ore with aboutl).05% Zn 632 kg. German ore containingl traces of Zn 64kg. scrap iron 220 kg. limestone 229 kg. coke The zinc Ycontent of the flue dust used for the sintered products is 0.3%, the iron content 43%. The remaining components of the ue dust ,are coke dust and slag particles.V Y

'I'he roasted pyrites used contain l0.20% ZnA and about4 60% Fe, and slag.

Y The reduction of the smelting charge'in the blast furnace is `carried out in a conventional manner and Y under conditions of temperature etc. commonly known in the art. The composition of the resulting pig -iron is also conventional.

part of roasted.

The first step of the process yields:

1000 kg. pig iron 7 93 kg. slag 101 kg. coarse ue dust 91 kg. ue dust slurry 1 1 kg. waste pig iron The coarse ilue dust containing about 0.4% Zn is re- In step II the charge for the rotary kiln is composed of 50 parts of roasted pyrites and 50 parts of flue dust slurry; no iron ores are added to the composition. 28 parts of fine-grained coke are added to the charge, the consumption of fuel being about 6% of the total dry weight of the charge. The iron nodules obtained from the kiln have the following average composition:

turned toV the blast furnace, the flue dust slurry, rich in zinc and other volatilizable metals, is used in the second 10 Fe s P C Scllv step of the process. ponens Step 11.-Ihe charge for the rotary kiln is prepared fiom ue dust slurry: German Ore and Toasted Pyrites- Percent Percent Percent Percent Percent The composition of each of these materials is determined 9279 1-05 165 038 4'57 by analysis to be the following:

Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent Percent Fe zn o Stor A1203 Gao Mgo Mn s P Hgo Flue Dust Slnrry 29. 5 2. 1 8. 7 .6 5. l 11.1 2. 8 20 German Ore 36.3 traces 43. 1. 47 0.90 0.26 0.10 0.015 0.19 6.6 Roasted Pyntes 43. 10.6 14.95 4.13 2.7 0.87 0.71 0.035 6.2

These materials are mixed to obtain a charge com- The amount of zinc obtained by this step corresponds posed of; to a rate of yield of 98%, the amount of iron to a yield rate of 92%. g3 prr The process according to our invention makes it poslop t b d ht f G n r hah om traces sible to separate iron and the volatilizable metals accompar.s y ry Welg o ema o e l g y panying iron and Waste materials containing iron from of Zmc one another in a continuous operation While at the same 29 parts of ne-grained coke having a particle size time profitably exploiting the presence of unconsumed below 4 millimetres are admixed to the composition. carbon in the ilue dust and flue sludge for the reduction The rotary kiln is heated with coal dust. The amount process. Furthermore, we succeed, by the process acof heating fuel required is equal to about 7% of the dry cording to our invention, in favorably complementing the Weight of the charge. The temperature in the hottest various raw materials in the process by other components zone of the kiln is maintained at about l250 C. The to obtain a balanced charge in which iron nodules obtained by the second step have the follow- (a) The low content of metals in the line dust or ing average composition: ue sludge is increased by the addition of Waste materials from foundries, steel Works, and the like to a level making Slag the entire process economically profitable; and Fe s P C com (b) A calcium oxide content above normal in the ponents sludge obtained from the flue dusts permits the application of the Krupp direct process even to foundry Waste Percent Percent Percent Percent Permit materials rich in silicio acid, because a favorable ratio 94'12 0'92 0' 68 042 2'76 of the components in the resulting slag is hereby obtained without substantially impairing the iron output or con- The amount of iron produced by this process corre- Sqllelfy raSiIlg the COS O the prOCeSS. Sponds to a rate of yield of 94%, the yield of Zinc is 50 The process according to our invention is therefore 97 7% suitable for making those iron and metal production Example 2 methods more economical in which Waste materials of the In Step I a charge for he production of 1000 kg' of nature described as being adapted for use in this process pig iron is prepared in the same manner as in Example 1. .are a nal (ir mtimedlary produc? The Process accord' The content of zinc from the flue dust in the sintered prod- D mg to The .Invention can be applied to procsses of the uct is 05%, the iron content of ,the same 38% The aforesaid kind as a part of a cycle of operation, thereby roasted pyrites used for preparing the sintered product reducmg the 1058.65 of on .39d accompanying. metals m contain 3% of Zinc and about 56% of iron. The amounts the total Cycle Wlhout requiring costiy prehimnary sps of products obtained by the rst step of this process are of processlilg The ratas of Producuon of on and the not Substantially changei accompanying metals can be so adapted to each other In step u the charge for the rotary kiln has the fob in the total cycle of operation that the highest degree of lowing composition: economy possible is achieved. i

Apart from the above-described advantages, the two- 55 Parts bY dfY Weight 0f TOaS PYTCS step process according to our invention offers the further 25 Parts by Cby Weight 0f bue dust Sblfly 65 advantage that the finely divided portion in the ores to 9 Parts by QTY Welgbl 0f Gemal'l Ore, cbl'falbmg Only be used for the process need not be converted to a traces 0f 2111 coarser form for introduction into the blast furnace step, The treatment of this mixure in the rotary kiln is but can be introduced directly in its finely divided form substantially identical with that of Example l. The mt@ the Second SeP- amount of iron produced corresponds to a rate of yield of Fbtbbfmofe, Slags, Waste 0f burnt 0I wasted Orb, 915%that ofzincto 98 1%c Waste from orgings, residues in the form of dust and similar Waste material which cannot be used by them- Example 3 selves due to their chemical composition and/or their Step I is carried out in the same manner and with the physical nature for processing either in a blast furnace same quantities of materials as in Example 1. or in a rotary kiln, can now be processed by introducing f 7 them'at'a suitable moment into the process according to our invention. y Y *i When applying the process laccording to Kour, invention injconnection with a` blast furnace operation, it Vnow becomes possible to process in the blast furnace ores and Waste materials which contain, apart from the iron, volatilizable non-ferrous metals, in particular lead rand zinc, in a considerably higherrproportion than was hitherto possible without suffering any loss of iron'or accompanying metals, or shortening unduly the ,lifetime of the blast furnace, and consequently with increased economic bene-` lits. It is'. also an advantage ofthe new process that subsequent processing of the flue dust obtained `from the blast furnace treatment in a rotary kiln instead of returning the flue dust to the blast furnace process, leads to a substantially smaller development of gas escaping from the rotary kiln than is being developedin the blast ,K

furnace. This is due, atleast partly, to Ythe fact that a much smaller quantity of flue dus't is being processed inV the rotary kiln as compared with -the large' amountofY ores treated in the `blast furnace. VlItis evidently much simpler to recover the volatilizable metals from the smaller kiln gas volume 'rather than fr'ormfthe' large vvolume of blast furnace top gas.

It will be understood that this invention is susceptible to modification in order to adapt it to different usages and conditions and, accordingly, it isdesire'd-to compre-v waste material in a blast furnace to form pig iron, and aV second step of reducing a charge comprising the flue dusts from said blast furnace step and sludge obtained from f said flue dusts, in a rotary kiln, said flue dusts and sludge containing compounds of iron as well as of said volatilizable metals, which iron compounds are reduced to iron during said second step, and recovering volatiliz'able metalsV from the Vwaste gases.

`2. A process according to claim 1 characterized by said volatilizable metals comprising lead and zinc. Y

3. A process according to claim l characterized by the step of introducing a portion of said ores and waste materials directly into said second process step.

4. A process according to claim 1V characterized in that said ores and Waste materials Ycomprise a fine-grained portion, which portion is introduced'directly into said second process step. 4

5. A process for separating iron from metalsraccompanying iron in ores and Vwaste materials, which accompanying metals are volatilizable during the reduction of iron, comprising a first step vof smelting the ores and waste materials in a blast furnace to form pig iron, a second step of reducing a charge comprising the ue dusts from said blast furnace step `and sludge obtained from said ue dusts, which flue dusts and sludge contain compounds of iron as ,Well as said volatilizable metals, Vn a rotary kiln, thereby reducingV said ironcornpounds Yto iron under thetformation of slag and waste*V andV expelling said volatilizable metals in said VWaste'` Ygases containing said volatlizable metalsrfro'm saidnkilmY andV the step of recovering said volatilizable'nietals fronisaid Wasteggases. Y Y 6.fA,proces's according to claim-5 characterizedby adding, at will, admixtures off from a high silicic acid to Y a high basic content to said chargezto ,be treated by said second step in order to obtain a slagof a determined composition.; Y Y

Y 7. A process for separating iron from metals accom; panying iron in ores and waste materials, which accom- Y panying metals are volatilizable during the vreduction of iron, comprisingra rst step of smelting the ores and waste material in a blast furnace to form pig iron, and a second Y,step of reducinga charge Vcomprising the flue dust'sfro'm" saidblast furnace step and sludge obtainedV from said ue dusts, in a, rotaryvkiln, vby the directsmelting fof aV charge containing ferriferous ores mixed with reducing agents and introduced into one edofsaid kiln and at the opposite end of said kiln Vby-preheating,'reduction Vto iron sponge and lumping of the iron sponge inA the dammed up charge adjacentsaid opposite kiln end, said flue dusts and sludgecontaining compoundsofiron Well as of said volatilizable metals, which iron compounds are reduced to iron duri/ng said second step, said volatilizable metals being subsequently recovered from the jwaste gases of said second step by methods known perse. n ,Y Y

8.v A process for separating iron from metals accompanying iron in ores and waste materials, which accompanying metals are'volatilizable during the reduction of iron, comprising a rst step of smelting the ores and Waste -Y material in a blast furnace to form pig iron, and a second step of reducing a charge comprising theV flue dusts'from said blast furnace step and sludge obtained from said flue dusts, in a rotary kiln, said flue dusts and sludge containing compounds of iron aswell as of said yolatilizable metals, which iron compounds are reduced to iron during said second step, introducing diicultly reducible materials into said second step together With said ue dusts and sludge obtained from the latter, and Vrecovering volatilizt able metals from the waste gases. Y s Y 9. A process -as'descn'bedin claim 8,'-characterized in 'Y that said diicultly reducible materials are roasted pyrites.

References Cited in the le of this patent UNITED STAT-ES PATENTSV 1,431,877 Diehl oct. 10,1922 1,517,232 Diehl NOV. 25,Y 1924 1,789,932 A smaiu f A f 12111.20, 1931 VV2,011,400 Eulenstein V V.. Y Aug. 13, `1935 2,373,244 Holz Apr. 10, 1945 V2,598,743 Waring et al. June 3, 1952 2,631,178 Y Morton a Mar. 10, 1953 FOREIGN PATENTS l 480,566

Great Britain 1st-n.24, 193s 

1. A PROCESS FOR SEPARATING ION FROM METALS ACCOMPANYING IRON IN ORES AND WASTE MATERIALS, WHICH ACCOMPANYING METALS ARE VOLATILIZABLE DURING THE REDUCTION OF IRON, COMPRISING A FIRST STEP OF SMELTING THE ORES AND WASTE MATERIAL IN A BLAST FURNACE TO FORM PIG IRON, AND A SECOND STEP OF REDUCING A CHARGE COMPRISING THE FLUE DUSTS FROM SAID BLAST FURNACE STEP AND SLUDGE OBTAINED FROM SAID FLUE DUSTS, IN A ROTARY KILN, SAID FLUE DUSTS AND SLUDGE CONTAINING COMPOUNDS OF IRON AS WELL AS OF SAID VOLATILIZ- 